Two-dimensional transition metal dichalcogenides (TMDs) have attracted enormous
interest due to the richness of their optical and electronic properties. Here, we consider
two prototypical two-dimensional TMD metal-semiconductor bilayer heterostructures,
VSe2-MoSe2 and VSe2-WSe2, and investigate the effect of the semiconducting layer
on the plasmons supported by the metallic layer using first principles time-dependent
density-functional theory (TDDFT). We focus on the flat regime of the plasmon
dispersion where momentum transfer is larger than 0.05 Å-1 and the interband
transitions gain importance. With the addition of the semiconducting layer, we show
that the electronic band structure undergoes significant changes close to the Fermi
level and hybridization occurs, which leads to strengthening of the interband transitions
and a significant red-shift in the plasmon energy.